Electric connector with an elastically deformable contact pin

ABSTRACT

An IC socket includes a contact pin having a plate-like shape. The IC package has a solder ball, and the side surface of the contact portion is separated from the side surface of the solder ball. The contact portion is thinned at its central portion as compared with the edge portions, and the inclined surfaces contact but are separate from the solder ball. Normal lines of the contact points of both the inclined surfaces are directed to the center of the solder ball. The solder ball is received in the thinned portion thereof. In this way, a location space is narrowed in comparison with a flat plate contact pin. The solder ball is also guided by a pair of inclined surfaces to locate it in the predetermined position, and form a wiping effect.

TECHNICAL FIELD

The present invention relates to a contact pin having an improvedstructure adapted to contact to and separate from a spherical terminalof an electronic part such as semiconductor, (called IC packagehereinlater) and an improved electric connector using the contact pin.

BACKGROUND ART

As a conventional one of such contact pin, there is provided the contactpin, for example, shown in FIGS. 18 and 19 (see Japanese Utility ModelLaid-open Publication No. SHO 60-109272). A contact 1 corresponding tosuch "contact pin" is formed of a sheet of metal plate by bending thesame, and a pair of contact pieces 2 and 3 are formed to the contact 1.As shown in FIG. 19, a rod-like pin terminal 4 is inserted between boththe contact pieces 2 and 3 and an electrical connection is establishedthrough the contact of the pin terminal 4 to the contact pieces 2 and 3.

In more detail, one 2 of the contact pieces is formed with a slitportion 2a and the other one 3 thereof is formed with a cut-standportion 3a. The rod-like pin terminal 4 contacts respective cornerportions 2b and 3b of these slit portion 2a and theut-stand portion 3ato thereby establish the electrical conduction therebetween.

However, in such conventional structure of the distance L is not madeshort so much.

Furthermore, when the positional relationship between the pin terminal 4and the contact pieces 2 and 3 at a portion at which such contact 1 isarranged, a is shifted, the pin terminal 4 cannot contact exactly to thecorner portions 2b and 3b of the contact pieces 2 and 3, which mayresult in the lowering of the electrical conduction performance.

Then, the present invention has an object to provide a contact pin andan electric connector having advantage in location space and ensuringthe electrical conduction performance.

DISCLOSURE OF THE INVENTION

In order to achieve the above object, according to the presentinvention, there is provided a contact pin having a long plate shape inwhich a contacting portion formed to a front end portion thereof iscontacted to and separated from side surfaces of a spherical terminal ofan electric part through an elastical deformation of the contact pin,the contact pin being characterized in that the contacting portion has acentral portion having a thickness less than that of both side edgeportions in a width direction thereof, two inclining surfaces are formedto the contacting portion so as to be contacted to and separated fromthe spherical terminal, and tangential lines at contacting portions ofboth the inclining surfaces and the spherical terminal are directed tothe center.

According to this structure, since the central portion of the contactpin is made less in thickness than that both the side edge portionsthereof in the width direction and the inclining surfaces are formed,the spherical terminal is inserted into the thin thickness portion, sothat a space is reduced in comparison with a flat shape contact pin.Furthermore, according to the provision of the inclining surfaces, thespherical terminal is guided therealong to precisely locate thespherical terminal to a predetermined position, and moreover, throughthe sliding motion of the spherical terminal along the incliningsurfaces, the wiping effect can be achieved.

In a preferred embodiment, the inclining surface is formed only to thefront end contacting portion.

According to this structure, in addition to the above effect, thesectional secondary moment can be made large by forming the incliningsurface only to the contacting portion, thereby reducing the twistingand flexing functions, thus making large the contact pressure betweenthe spherical terminal and the contact pin.

In a further preferred embodiment, the front end portion is formed so asto provide two-fork shape as branched pieces to which the incliningsurfaces are formed respectively.

According to this structure, in addition to the above effects, thewiping effect can be further improved because the flexing force as wellas twisting force is caused to the respective branched pieces.

In a further preferred embodiment, each of the branched pieces of thefork shaped portion has a root portion having a width narrower than thatof a portion of the contacting portion side.

According to this structure, in addition to the above effects, therespective branched pieces are twisted largely by making narrow thewidth of the root portion, thereby further improving the wiping effectand it becomes effective in a case of small contact pressure between thecontact pin and the spherical terminal.

In a further preferred embodiment, each of the branched pieces of thefork shaped portion has a width gradually reducing from a root portiontowards a front end portion thereof and the inclining surface is formedfrom the root portion to the front end portion.

According to this structure, in addition to the above effects, thesectional secondary moment can be gradually changed by forming each ofthe branched pieces of the fork shaped portion to have a width graduallyreducing from a root portion towards a front end portion thereof andforming the inclining surface from the root portion to the front endportion, so that the stress distribution at respective positions of thebranched pieces can be made substantially equal and the concentration ofthe stress can be prevented.

In another aspect of the present invention, there is provided anelectric connector in which a contact pin having a long plate shape isdisposed on a connector body, a movable plate adapted to elasticallydeform the contact pin when horizontally moved is disposed to behorizontally movable, an upper operation member is disposed on an upperportion of the connector body to be vertically movable, when the upperoperation member is lowered, the movable plate is horizontally movedthrough a link mechanism to thereby elastically deform the contact pinand then displace the same and a spherical terminal of an electric partis thereby inserted under non-pressure contact condition to the contactpin, and when the upper operation member is moved upward, the movableplate is returned to an original position and the elastical deformationof the contact pin is then released, thereby contacting the front endcontacting portion of the contact pin to the side surface of thespherical terminal of the electric part to establish an electricalconnection, the contact device being characterized in that saidcontacting portion has a central portion having a thickness less thanthat of both side edge portions in a width direction thereof and contactpin is formed so as to provide two-fork shape having branched pieces, towhich inclining surfaces are formed respectively so that tangentiallines at contact points to the spherical terminal are directed to thecenter.

According to this structure, since the central portion of the contactpin is made less in thickness than that both the side edge portionsthereof in the width direction thereof and the inclining surfaces areformed, the spherical terminal is inserted into the thin thicknessportion, so that a space is reduced in comparison with a flat shapecontact pin. Furthermore, according to the provision of a pair ofinclining surfaces, the spherical terminal can be guided to therebylocate it to the predetermined position, and through the sliding motionof the spherical terminal along the inclining surfaces, the wipingeffect can be achieved. Furthermore, by forming the contact pin so as toprovide two-fork shape, since the twisting and flexing functions arecaused to the respective branched pieces thereof, the wiping effect canbe further improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents a contact pin and solder ball according to a firstembodiment 1 of the present invention, in which FIG. 1(a) is a plan viewand FIG. 1(b) is a sectional view.

FIG. 2 is a perspective view of an upper portion side of the contact pinof the first embodiment 1.

FIG. 3 is a front view of the contact pin of the first embodiment 1.

FIG. 4 is a plan view of an IC socket of the first embodiment 1.

FIG. 5 is a front view, half in section, of the IC socket of the firstembodiment 1.

FIG. 6 is a right side view as sectional view of FIG. 5 concerning thefirst embodiment 1.

FIGS. 7a through 7c are sectional views showing a relationship between amovable plate and the contact pin according to the first embodiment 1.

FIG. 8 represents a latch and the like and the contact pin concerningthe first embodiment 1, in which FIG. 8(a) is a view showing a state ofsupporting the IC package and FIG. 8(b) is a view showing a state of theIC package released.

FIG. 9 is a schematic view showing a link mechanism of the IC packageaccording to the first embodiment 1, in which FIG. 9(a) is a viewshowing a state before the lowering of an upper operation member andFIG. 9(b) is a view showing a state after the upper operation member islowered.

FIGS. 10a through 10C are plan views explaining an operation of thecontact pin and the solder ball according to the first embodiment 1.

FIGS. 11a and 11b are plan views showing the contact pin and the solderball according to the first embodiment 1.

FIG. 12 is a view showing the contact pin and the solder ball accordingto the first embodiment 1, in which FIG. 12(a) is a plan view and FIG.12(b) is a sectional view.

FIG. 13 is a plan view explaining an operation of the contact pin andthe solder ball according to the first embodiment 1.

FIG. 14 is a view showing a contact pin according to a second embodiment2, in which FIG. 14(a) is a plan view and FIG. 14(b) is a front view.

FIG. 15 is a view showing a contact pin according to a third embodiment3, in which FIG. 15(a) is a plan view and FIG. 15(b) is a front view.

FIG. 16 is a view showing a contact pin according to a fourth embodiment4, in which FIG. 16(a) is a plan view and FIG. 16(b) is a front view.

FIG. 17 is a view showing the contact pin and a solder ball according tothe fourth embodiment 4, in which FIG. 17(a) is a plan view and FIG.17(b) is a front view.

FIG. 18 is a perspective view showing a conventional contact.

FIG. 19 is a sectional view of the conventional contact.

BEST MODE FOR EMBODYING THE INVENTION

The exemplary embodiments of the present invention will be describedhereunder.

[Exemplary Embodiment 1]

FIGS. 1 to 13 represent a first exemplary embodiment 1.

The structure of the first exemplary embodiment 1 will be firstdescribed hereunder with reference to FIGS. 4, 5 and 6, in whichreference numeral 11 denotes an IC socket as an "electric connector" andthe IC socket 11 serves to establish an electrical connection, forcarrying out a performance test of an IC package 12 as an "electricpart", between a solder ball 12b as "spherical terminal" of the ICpackage 12 and a printed wiring board, not shown, of a tester.

The IC socket 11 generally comprises a socket body 13 as a "connectorbody" to be mounted on the printed wiring board. A rectangular movableplate 14 is disposed on the socket body 13 to be horizontally movable ina predetermined direction, and a contact pin 19 provided for the socketbody 13 is made elastically deformable through the horizontal movementof the movable plate 14. An upper plate 16 is disposed in a fixed stateto the socket body 13 on the upper side of the movable plate 14, andfurther on the upper side thereof, an upper operation member 17 having arectangular frame structure is disposed to be vertically movable in amanner such that when the upper operation member 17 is vertically moved,the movable plate 14 is horizontally moved through an X-shaped link 18.

In more detail, the contact pin 19 is formed of a material having aspringy property and excellent electric conductivity so as to provide anelongated plate shape, and as shown in FIGS. 5 and 6, the contact pin 19is press fitted into the socket body 13. A lead portion 19a projectsfrom the lower surface of the socket body 13 and is electricallyconnected to the printed wiring board. Furthermore, an upper sideportion (tip end side portion) of the contact pin 19 projecting over theupper surface of the socket body 13 is inserted into an insertionportion 14b of the movable plate 14 and a through hole 16b formed to theupper plate 16. The tip end side portion of the contact pin 19 has athinner central portion than both side edge portions in its widthdirection, as shown in FIGS. 1 and 2, so as to provide a fork-shapehaving branched pieces 19b, 19b having inclining surfaces 19c, 19c,respectively. These inclining surfaces 19c, 19c have tangential lines atcontact points to the solder ball 12b directing to the center thereof.When the movable plate 14 is horizontally moved in an arrowed directionfrom the state shown by FIG. 7(a) to the state shown by FIG. 7(b), thecontact pin 19 is pressed by a pressing portion 14a of the movable plate14 and then elastically deformed, whereby the solder ball 12b in the ICpackage 12 is made insertional into the through hole 16b of the upperplate 16. Thereafter, when the movable plate 16 is returned in anarrowed direction in FIG. 7(c), the contact pin 19 contacts the solderball 12b of the IC package 12 to thereby establish the electricalconnection.

Furthermore, the upper plate 16 has a rectangular shape and is disposedon the upper side of the movable plate 14 in a state that a plurality ofpositioning bosses, not shown, projecting from the socket body 13 arefitted to recessed portions formed at corner portions of the rectangularupper plate 16. The movable plate 14 is provided with idle insertionportions into which the positioning bosses are idly inserted so that theidle insertion portions each has a size allowing the movable plate 14 tohorizontally move without interfering the positioning boss when movedhorizontally. The upper plate 16 is provided with a plurality of throughholes 16b, each having a rectangular shape, into which the solder ball12b of the IC package 12 is inserted, at portions corresponding to theinsertion portions 14b formed to the movable plate 14 and also providedwith four guide portions 16c for positioning the IC package 12 at themounting time thereof at portions corresponding to four corner portionsof the IC package 12, respectively.

The upper operation member 17 has a rectangular frame structure, asshown in FIG. 4, having an opening 17a of a size enabling the IC package12 to be inserted therein, and the IC package 12 is inserted through theopening 17a and mounted on the upper plate 16. Further, the upperoperation member 17 is disposed to the socket body 13 to be verticallymovable through a slide portion 17b. As shown in FIG. 6, the upperoperation member 17 is urged upward by means of spring 20 disposedbetween the upper operation member 17 and the socket body 13.

The X-shaped link 18 mentioned before is disposed to each of both endportions in the moving direction of both side surfaces along the movingdirection of the rectangular movable plate 14. That is, in thisembodiment, four X-shaped links 18 are disposed corresponding to boththe end portions of both the side surfaces of the movable plate 14 tothereby constitute a toggle joint structure.

More concretely, each of the X-shaped links 18 is composed of first andsecond link members 23 and 25 both having the same length and connectedwith each other to be rotatable through a central connection pin 27.

The first link member 23 has a lower end portion 23b which is connectedto the socket body 13 to be rotatable through a lower end connection pin29, while the second link member 25 has a lower end portion 25b which isconnected to one end portion of the side surface of the movable member14 along the moving direction thereof to be rotatable through a lowerend connection pin 30. These first and second link members 23 and 25have upper end portions 23c and 25c which are connected to the upperoperation member 17 through upper end connection pins 33 and 34respectively to be rotatable. The upper end connection pin 33 providedfor the upper end portion 23c of the first link member 23 is insertedinto a slit 17c elongated in the horizontal direction formed to theupper operation member 17 to be movable in the horizontal direction.

Further, as shown in FIGS. 6 and 8, a latch 35 is disposed to the socketbody 13 to be rotatable about a shaft 35a disposed at the lower endportion of the latch 35 so as to be engageable with a side edge portionof the IC package 12 set to the predetermined position and the shaft 35ais urged by the spring 36 in an engaging direction. The upper operationmember 17 is formed with a cam portion 17d sliding along the latch 35 atthe lowering time thereof and rotating it in a disengaging direction.

In FIG. 5, reference numeral 38 denotes a location board performing apositioning function at the time of mounting to the printed wiringboard.

The IC socket 11 of the structure mentioned above is used in thefollowing manner.

A plurality of IC sockets 11 are preliminarily disposed on the printedwiring board by inserting the lead portions 19a of the contact pins 19of the IC sockets 11 through the insertion holes of the printed wiringboard and the inserted ends are then soldered.

The IC package 12 is set in the IC socket 11 by, for example, anautomatic machine and then electrically connected thereto in thefollowing manner.

That is, in a state of holding the IC package 12 by the automaticmachine, the upper operation member 17 is pressed downward to lower thesame against the urging force of the spring 20. Then, as shown in FIG.8(b), the latch 35 is rotated against the urging force of the spring 36by the cam portion 17d of the upper operation member 17 and the latch 35is retired from the insertion range of the IC package 12. At the sametime, the movable plate 14 is horizontally moved by the operation of theX-shaped links 18, and through this horizontal movement, the contact pin19 is pressed by the pressing portion 14a formed to the movable member14 and elastically deformed (see FIG. 7(b)). In this state, the solderball 12b of the IC package 12 which has been held is inserted into thethrough hole 16b of the upper plate 16 to thereby release the IC package12 from the automatic machine.

Thereafter, when the pressing force of the upper operation member 17 bymeans of the automatic machine is released, the upper operation member17 is moved upward by the urging force of the spring 20 and the movableplate 14 is then returned to its original position. Through suchoperation, the contact pin 19 is returned by its elastic property and apair of inclining surfaces 19c, 19c at the upper end portion of thecontact pin 19 are electrically contacted and then connected to thesolder ball 12b of the IC package 12.

More in detail, under the state that the solder ball 12b is insertedinto the through hole 16b of the upper plate 16, in a case shown in FIG.10(a) in which the solder ball 12b is shifted from the center of thethrough hole 16b, the inclining surface 19c of one of the branchedpieces 19b of the contact pin 19 abuts against the side surface of thesolder ball 12b by returning the contact pin 19 (see FIG. 10(b)),whereby the solder ball 12b moves along the inclining surface 19c,thereby contacting the other inclining surface 19c, and hence, thesolder ball 12b abuts against both the inclining surfaces 19c, 19c withequal force, thereby establishing the electrically conductive state. Insuch manner, the solder ball 12b is positioned to the predeterminedposition (see FIG. 10(c)). Further, through such sliding motion of thesolder ball 12b along the inclining surfaces 19c, 19c, a wiping functionwill be achieved.

Under the state mentioned above, when the solder ball 12b is furtherpressed, a reaction force P due to the solder ball 12b acts in adirection perpendicular to the inclining surfaces 19c, 19c as shown inFIG. 12(a). In this moment, the branched pieces 19b, 19b of thefork-shaped contact pin 19 are flexed outward as shown with dash andtwo-dot-line in FIG. 12(b) by a component force P1 of the reaction forceP. Accordingly, the solder ball 12b slides along the inclining surfaces19c, 19c to thereby achieve the wiping function. Furthermore, twistingmoment is caused to the respective branched pieces 19b, 19b by thereaction force P as shown in FIG. 13 and the branched pieces are twistedas shown with dash and two-dot-line in FIG. 12(b). According to suchtwisting motion, the angles of the inclining surfaces 19c, 19c vary andthe direction of the reaction force P also varies to P2, and as aresult, the component force P2 is increased and accordingly theflexibility of the branched pieces 19b, 19b are also made large. As aresult, the wiping function can be further improved.

At the same time, the upper operation member 17 is moved upward and thelatch 35 is rotated in a direction reverse to the arrowed direction inFIG. 6 by the urging force of the spring 36 and engaged with the sideportion of the IC package 12, thus holding the IC package 12 (see FIG.8(a)).

The X-shaped links 18 for horizontally moving the movable plate 14 isexplained hereunder.

When the upper operation member 17 is lowered, the upper end portions23c and 25c of the respective link members 23 and 25 are presseddownward and then lowered from the state shown in FIG. 9(a) to the stateshown in FIG. 9(b), and then, the respective link members 23 and 25 arerotated to thereby horizontally move (in an arrowed direction) the lowerend portion of the second link member 25 and hence horizontally move themovable plate 14 in the arrowed direction.

As mentioned hereinbefore, the central portion side of the contact pin19 is made thinner than both the side edge portions in the widthdirection thereof to thereby form the inclining surfaces 19c, so thatthe spherical solder ball 12b enters this thinner portion. Accordingly,the case shown in FIG. 11(b), in comparison with a case shown in FIG.11(a), in which any improvement is not applied to the contact pin 19having a flat surface, the through hole 16b of the upper plate 16 can bemade small by an amount corresponding to a size C. That is, it isnecessary for the through hole 16b of the upper plate 16 to have a sizecapable of receiving a solder ball 12b having the maximum radius and thecontact pin 19 so that various solder balls 12b having various sizes canbe inserted into the through hole 16b. However, in a case where aplurality of solder balls 12b support the IC packages 12 arranged with afine interval therebetween, it is required to make large a rib-distancebetween the through holes 16b in the viewpoint of strength, andaccordingly, it is necessary to make the size of the through hole 16b aspossible as small. In this viewpoint, it is extremely effective to makesmall the through hole 16b by the size C as mentioned above.

In the embodiment described above, the solder ball 12b can be preventedfrom disengaged upward with the solder ball 12b being held by theinclining surface 19c of the contact pin 19 and the peripheral edgeportion of the through hole 16b by forming a recessed portion, having asize capable of receiving a portion of the solder ball 12b, to a portionof the inclining surface 19c of the contact pin 19 contacting the solderball 12b or a portion of the peripheral edge portion of the through hole16b abutting against the solder ball 12b, whereby the IC package 12 canbe surely held. This mode will be applicable to the followingembodiments.

[Exemplary Embodiment 2]

FIG. 14 represents a second exemplary embodiment 2 of the presentinvention.

In this embodiment 2, the two-fork shaped branched pieces 19b each has aroot portion 19e having a width H smaller than that of a contact sideportion 19d thereof.

According to this structure, since the sectional secondary moment of theroot portion 19e of each of the branched pieces 19b is made small, whena reaction force is applied to the contact side portion 19d from thesolder ball side, the twisted and flexed amounts of the branched piece19b is made large in comparison with the case of the embodiment 1.Accordingly, the wiping effects can be improved.

The other structures and functions of the embodiment 2 are substantiallythe same as those of the embodiment 1.

[Exemplary Embodiment 3]

FIG. 15 represents a third exemplary embodiment 3 of the presentinvention.

In the embodiment 3, only the front end portion (contact side portion19d) of each of the two-fork shaped branched pieces 19b is formed withthe inclining surface 19c.

According to this structure, since the branched piece 19b provides as awhole a large sectional secondary moment, the twisted and flexed amountsof the branched piece 19b can be made small in comparison with theembodiment 1, so that it is effective to make large the contact pressurebetween the solder ball 12b and the contact pin 19.

The other structures and functions of the embodiment 3 are substantiallythe same as those of the embodiment 1.

[Exemplary Embodiment 4]

FIG. 16 represents a fourth exemplary embodiment 4 of the presentinvention.

In this embodiment 4, each of the two-fork shaped branched pieces 19b isformed such that the width H thereof is made gradually narrow towardsthe front end portion from the root portion 19e thereof and theinclining surface 19c is formed from the root portion 19e to the frontend portion.

According to this structure, since the sectional secondary moment of thebranched piece 19b is gradually changed, the stress distribution of eachof the branched pieces 19b can be made substantially equal at therespective positions and the concentration of the stress can beprevented.

The other structures and functions of the embodiment 4 are substantiallythe same as those of the embodiment 1.

[Exemplary Embodiment 5]

FIG. 17 represents a fifth exemplary embodiment 5 of the presentinvention.

A contact pin 29 of this embodiment 5 is formed with a U-shaped portion31 at its upper side portion and each leg portions of this U-shapedportion 31 are each formed to provide two-fork shape, thus providingtotally four branched pieces 32. These branched pieces 32 are eachformed with an inclining surface 32a as in the embodiment 1.

In the structure of this embodiment 5, the solder ball 12b is insertedinto the fork shape portions of the U-shaped portion 31, which is hencewidened through an elastical deformation, whereby the solder ball 12bcontacts the respective inclining surfaces 32c.

In the respective exemplary embodiments mentioned above, although the"contact pin" of the present invention is applied to the contact pin 19of the IC socket 11, the contact pin is not limited to it and may beapplicable to contact pins of other devices, and furthermore, althoughthe contact pin is applied to the IC socket 11 as "electric connector",it may be applicable to other devices which achieve the function of anelectrical connection.

Furthermore, in the above exemplary embodiments, although the contactpin is formed so as to provide the two-fork shape, the present inventionis not limited to this shape and may take a structure such that thecentral side portion of the contact portion is formed thinner in thewidth direction in comparison with both the side edge portions and atleast two inclining surfaces contacting to and separating from thespherical terminal are formed so that both the tangential lines at thepoints contacting the spherical terminal are directed to the centralportion thereof. In this structure, the two inclining surfaces willprovide a continuous "<" shape. Further, the inclining surface may beformed to provide a flat surface or curved surface.

Possibility of Industrial Usage

As mentioned above, the contact pin according to the present inventioncan be preferably applied to a contact pin of an IC socket. It is ofcourse applicable to contact pins of other devices. Furthermore, theelectric connector according to the present invention can be preferablyused as an IC socket into which IC packages can be detachably mounted,which is of course applicable to other devices which attain the functionof the electrical connection.

What is claimed is:
 1. A contact pin adapted to contact a side surfaceof a spherical terminal of an electric part, comprising:two contactingportions, each having an edge portion, said edge portion having athickness; a central portion between the two contacting portions, saidthickness of the central portion being less than said thickness of eachof the edge portions; and each of said contacting portions comprising aninclined surface adapted to contact a side surface of the sphericalterminal, and wherein, while the two inclined surfaces of the twocontacting portions of the contact pin are contacted to the side surfaceof the spherical terminal so that current flows through the contactingportions of the contact pin into the spherical terminal of the electricpart, normal lines at contact points at which the inclined surfaces andthe side surface of the spherical terminal are contacted are directed toa center of the spherical terminal.
 2. The contact pin according toclaim 1, wherein each of said contacting portions has a front endportion and each of said inclined surfaces is formed only on the frontend portion of the corresponding contacting portion.
 3. The contact pinaccording to claim 1, wherein each of said contacting portions has afront end portion, and the front end portions are formed so as toprovide two-fork shaped branched pieces, to which the inclined surfacesare formed respectively.
 4. The contact pin according to claim 3,wherein each of said branched pieces is provided at its one end sidewith a contact portion and its other end side with a root portion, eachof said contact portions being adapted to contact the side surface ofthe spherical terminal and having a width, said root portion having awidth which is narrower than the width of the corresponding contactportion.
 5. The contact pin according to claim 3, wherein each of saidbranched pieces has a width and is provided at its one end side with acontact portion and its other end side with a root portion, said contactportion being adapted to contact the side surface of the sphericalterminal, said width gradually reducing from the root portion towardsthe contact portion, said each of the inclined surfaces being formed toextend from the root portion to the contact portion.
 6. An electricconnector for an electrical part having a spherical terminal, saidelectric connector comprising:a connector body; a contact pin disposedon the connector body and formed as a long plate shape, said contact pinhaving two contacting portions for contacting the spherical terminal,each of said contacting portions having a front end portion formed so asto provide two-fork shaped branched pieces; a central portion betweenthe two contacting portions, said central portion having a thickness; amovable plate disposed in the connector body to be horizontally movable,said movable plate being horizontally moved so as to elastically deformthe contact pin; an upper operation member disposed on an upper portionof the connector body to be vertically movable; and a link mechanismoperatively connected to the movable plate and the upper operationmember, wherein, when the upper operation member is moved downward, saidmovable plate is horizontally moved through the link mechanism therebyelastically deforming the contact pin and displacing the contact pin sothat the spherical terminal of the electric part is inserted in theconnector body while the spherical terminal is not pressed to fit to thecontact pin, and when the upper operation member is moved upward, saidmovable plate is returned to an original portion and the contact pin isreleased from an elastically deformation force of the movable plate sothat the contacting portion of the contact pin is contacted to a sidesurface of the spherical terminal to establish an electrical connection,each of said contacting portions of the contact pin comprising:an edgeportion having a thickness, said thickness of the central portion beingless than said thickness of each of the edge portions; and an inclinedsurface adapted to contact the side surface of the spherical terminalwherein, while the two inclining surfaces of the contact portions arecontacted to the side surface of the spherical terminal so that currentflows through the contacting portions of the contact pin into thespherical terminal of the electric part, normal lines at the contactpoints at which the inclines surfaces and the side surface of thespherical terminal are contacted are directed to a center of thespherical terminal.
 7. A contact pin adapted to contact a side surfaceof a spherical terminal of an electric part, comprising:two contactingportions, each having an edge portion, said edge portion having athickness; a central portion between the two contacting portions, saidthickness of the central portion being less than said thickness of eachof the edge portions; and each of said contacting portions comprising aninclined surface adapted to contact a side surface of the sphericalterminal and to be separated from the side surface thereof, and wherein,while the two inclined surfaces of the contact pin are contacted to theside surface of the spherical terminal so that current flows through thecontacting portion of the contact pin into the spherical terminal of theelectric part, the two inclined surfaces are directed to a center of thespherical terminal and extending lines inwardly extending along therespective inclined surfaces of the two contacting portions of thecontact pin are crossed to each other.
 8. The contact pin according toclaim 7, wherein each of said contacting portions has a front endportion and each of said inclined surfaces is formed only on the frontend portion of the corresponding contacting portion.